I was browsing Wikipedia and came upon three different variations for Ra's origins:

In the former version, a mound arises from the waters. An egg was laid upon this mound by a celestial bird. The egg contained Ra. In some variants, the egg is laid by a cosmic goose. However, the egg was also said to have been a gift from Thoth, and laid by an ibis, the bird with which he was associated.

Later, when Atum had become assimilated into Ra as Atum-Ra, the belief that Atum emerged from a (blue) lotus bud, in the Ennead cosmogony, was adopted and attached to Ra. The lotus was said to have arisen from the waters after the explosive interaction as a bud, which floated on the surface, and slowly opened its petals to reveal the beetle, Khepri, inside. Khepri, an aspect of Ra representing the rising sun, immediately turns into a weeping boy – Nefertum, whose tears form the creatures of the earth.

Ptah is rarely mentioned in the literature of Old Kingdom pyramids. This is believed by some to be a result of the Ra-worshipping people of Heliopolis being the main writers of these inscriptions. Followers of Ra were known to be jealous of Ptah. While some believed that Ra is self-created, others believed that Ptah created him.

Given Ra's popularity and central position in Egyptian mythology, I would have assumed his origin story would be somewhat standardized. Local variations are to be expected, of course, but I couldn't find any information on which one stood out - if any.

The actual process of creation was the interest of theologians in another great Egyptian city, Heliopolis (near the site of modern Cairo). Egyptian creation accounts do not seem to have envisaged the possibility of something being created from nothing. Instead, they describe how everything in the world-all its elements and forces-came from a single source, much like the primordial singularity in the "Big Bang" theory of modern physics. This original source of all things was known as the god Atum. The god's name means "finisher," and refers to the fact that Atum "finished up" as the world.

<snip>

The birth of the sun is actually the cumlination of creation in the Heliopolitan system, as it is in the early myth of the primeval mound. The sun's first rising into the newly created world-space marks the end of creation and the beginning of the eternal cycle of life, which the sun regulates (as king of nature) and makes possible through his heat and light. The Heliopolitan accounts therefore concentrate not only on Atum's "evolution" but also on the sun's role in the creation. An element of nature, the sun is known simply as "Sun" (usually trascribed "Re" or "Ra"). As the newly risen

Memphis had yet another interpretation which is very similar to that of Heliopolis, except that Ptah served as the intermediary through which Atum's will was given form:

But much older is Ptah, who enlivened all the gods as well as their life-forces through this heart and through this tongue ... His Ennead is in his presence in teeth and lips, which are the seed and hands of Atum: for Atum's Ennead evolved form his seed and his fingers, but the Ennead is teeth and lips in this mouth that pronounced the identity of everything and through which Shu and Tefnut emerged and gave bearth to the Ennead.

The Thebans did not reject the Ogdoad altogether, but placed Amun as its sole creator: he was the "First One Who Gave Birth to the First Ones." One version of the myth depicts him as a serpent, Amun-Khamutef ("He Who Has Completed his Moment"), living in the waters of Nun. However, it is suggested elsewhere that he emitted a mighty honk, like a goose, which burst into the stillness of the universe, causing a cosmic reaction by which the Ogdoad and the Ennead were formed.
The Thebans developed a distinct theology in which Amun was concealed even from the gods, existing somewhere beyond the natural world. It was thought that a creator had to stand apart from his creation, and Amun, the "hidden" god, suited this role. The texts summarized Amun's mystery and power:

"He is hidden from the gods, and his aspect is unknown. He is farther than the sky, he is deeper than the Duat. No god knows his true appearance ... no one testifies to him accurately. He is too secret to uncover his awesomeness, he is too great to investigate, too powerful to know. Manifest one, whose identity is hidden ... as it is inaccessible."